docs: def _load_cached_tlds(self):
          """
          Loads TLDs from cached file to set.
  
          :return: Set of current TLDs
          :rtype: set
          """
  
          # check if cached file is readable
          if not os.access(self._tld_list_path, os.R_OK):
              self._logger.error("Cached file is not readable for current "
                                 "user. ({})".format(self._tld_list_path))
              raise CacheFileError(
                  "Cached file is not readable for current user."
              )
  
          set_of_tlds = set()
          with open(self._tld_list_path, 'r') as f_cache_tld:
              for line in f_cache_tld:
                  tld = line.strip().lower()
                  # skip empty lines
                  if not tld:
                      continue
                  # skip comments
                  if tld[0] == '#':
                      continue
  
                  set_of_tlds.add("." + tld)
                  set_of_tlds.add("." + idna.decode(tld))
  
          return set_of_tlds